28312181 has 4 divisors (see below), whose sum is σ = 29002764. Its totient is φ = 27621600.

The previous prime is 28312177. The next prime is 28312187. The reversal of 28312181 is 18121382.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18121382 = 2 ⋅9060691.

It can be written as a sum of positive squares in 2 ways, for example, as 6838225 + 21473956 = 2615^2 + 4634^2 .

It is a cyclic number.

It is not a de Polignac number, because 28312181 - 2² = 28312177 is a prime.

It is a super-2 number, since 2×28312181² = 1603159185953522, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 28312181.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28312187) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 345230 + ... + 345311.

It is an arithmetic number, because the mean of its divisors is an integer number (7250691).

Almost surely, 2^28312181 is an apocalyptic number.

It is an amenable number.

28312181 is a deficient number, since it is larger than the sum of its proper divisors (690583).

28312181 is an equidigital number, since it uses as much as digits as its factorization.

28312181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 690582.

The product of its digits is 768, while the sum is 26.

The square root of 28312181 is about 5320.9191875089. The cubic root of 28312181 is about 304.7832590758.

The spelling of 28312181 in words is "twenty-eight million, three hundred twelve thousand, one hundred eighty-one".